Treatment of aromatic hydrocarbons with silica-alumina pills to produce solvents



Aprll 12, 1960 M ETAL 2,932,676

TREATMENT OF AROMATIC HYDROCARBONS WITH SILICA-ALUMINA PILLS TO PRODUCE SOLVENTS Filed June 8, 1956 AROHATICS DISTILLATION IHEAVIER FRACTIONS HYDROGEN REACTION ZONE I? g l2 HYDROFORMING ZONE REACTION ZONE NAPHTHENIG HYDROCARBON FEED INVENTORS. Elzo 0- Camp, Winfred 0- Milligon, BY Alberi J. Shmidl,

ATT'O United States ticularly, the invention is directed to the removal of color-forming bodies and the like from hydrocarbon solvents. In its more specific aspects, the invention is concerned with the treatment of aromatic hydrocarbon solvents to remove color-forming bodies therefrom.

The present invention may be briefly described as a method for producing low acid wash color hydrocarbon solvents by contacting a hydrocarbon fraction boiling within the range from about 150 to about 550 F. and having an acid wash color in excess of 4 with a silicaalumina catalyst at a pressure sufficient to maintain the liquid phase. The contacted hydrocarbon fraction is removed from the catalyst and then distilled to recover a distillate fraction having a low acid Wash color less than 4. The catalyst, having been used, is suitably regenerated by burning same employing a combustible mixture of. air and steam to support a combustion operation to remove from the catalyst contaminating bodies, such as resins, polymers, polar compounds, peroxides, and the like which tend to and do accumulate therein during the contacting operation. Thereafter the regenerated catalyst is reused to contact additional quantities of the hydrocarbon fraction.

The hydrocarbon fraction employed in the practice of the present invention suitably includes fractions boiling within the range of about 100 to about 550 F. Aromatic hydrocarbons boiling within the range of about 150 to about 550 F. and which have acid Wash colors greatly in excess of 4 may suitably be employed and the hydrocarbon fraction may be a benzene-containing fraction, a toluene-containing fraction or a xylene-containing fraction or aromatics higher boiling than xylenes in the range given. 1

The hydrocarbon fraction may also include parafiinic hydrocarbons which may be treated in accordance with the present invention to remove the deleterious bodies. Other hydrocarbons, such as naphthenic hydrocarbons, suitably may form the feed stock of the present invention. For example, cyclohexane fractions may be treated to remove contaminating unsaturated material, such as aromatic hydrocarbons and olefins. Likewise, aliphatic solvents may be treated to remove compounds which impart an undesirable odor to the solvent. For example, a hexane fraction may be treated to remove odor or odorforming bodies.

Where paraffiuic and naphthenic fractions are employed as the feed and the paraflinic and naphthenic fractions are free of aromatic hydrocarbons, it may be desirable to add a sufficient amount of an aromatic fraction or compound to the paraffinic or naphthenic fraction prior to charging atent same to the contacting step. An amount of aromatic compound sufiicient to react with the olefinic material or other contaminating or deleterious material may be employed.

If the feed fraction normally contains aromatic hydrocarbon, the amount thereof may be controlled by adjustment'and control of the fractional distillation operation by Way of which the feed fraction is obtained.

The catalyst employed in the present invention is suit ably a solid acid catalyst containing a major amount of 2,932,676 Patented Apr. 12, 1960 silica. As examples of the catalysts suitable for the present invention are the so-called silica-alumina catalysts which contain approximately 60 to percent by weight of silica and approximately 15 to 20 percent by weight of alumina. Catalysts which have been found suitable in the practice of the present invention include the so-called Filtrol clay and Attapulgus clay. Other similar clays may be used, such as floridan, and the like. Filtrol and Attapulgus clays give especially desirable re- 'sults. A typical analysis of dry Filtrol clay suitable for employment in the practice of the present invention is as follows: 74% by weight SiO 17.5% by weight A1 0 4.5% by weight MgO, 1.4% by weight of Fe O and 2.6% by weight of other compounds. Attapulgus clay contains approximately 67% SiO and minor amounts of alumina, magnesia and iron oxide.

The catalyst may suitably be employed as pills in a fixed bed or may beused as a slurry or suspension. It is preferred to employ a fixed bed employing pills of catalyst of about inch size.

The feed hydrocarbon contacts the catalyst in the liquid phase at a pressure sufiicient to maintain a liquid phase, such pressures ranging from about 400 to about 600 pounds per square inch gauge. Suitable pressure may range from about 450 to about 500 pounds per square inch gauge. A liquid phase on the catalyst is believed to maintain the catalyst clean and to prevent the accumulation of deleterious bodies.

Temperatures employed may range from about 400 to about 600 F. with suitable results being obtained at about 520 F. with predominantly aromatic fractions. With aliphatic fractions, temperatures of about 400 to 500 F. are preferred.

The feed stock contacts the catalyst at a liquid space velocity in the range from about 0.25 to about 5 volumes of feed per volume of catalyst per hour. A preferred liquid space velocity may be in the range from about 0.5 to about 1.5 v./v./hr.

It is desirable to regenerate the catalyst after about 2,000 barrels or more of feed stock has contacted each ton of the catalyst and thereafter to regenerate the catalyst by a burning operation wherein a mixture of air and steam is employed, the catalyst being burned at a temperature of about 800 to about 1000 lF., preferably 900 F. The amount of air and steam may be varied in the range from about 0 to /2 mole of air per mole of steam. In the regeneration, steam is passed through the bed to equilibrium, air is then admitted with the steam, increasing the air as regeneration proceeds. The temperature rise during regeneration is never allowed to be more than 200 F. After the amount of feed stated has contacted the catalyst, an amount of about 2% by Weight of polar compounds and other contaminating bodies has accumulated on the catalyst and should be burned off to insure best results. Burning of the catalyst does not affect its activity deleteriously and the regenerated catalyst is suitably reused in the process to obtain beneficial results. i

In order to illustrate the invention further, reference will now be had to the drawing in which the single figure is in the forin of a diagrammatic flow sheet of a preferred mode.

Referring nowto the drawing, numeral 11 designates a charge line by way of which a naphthenic hydrocarbon fraction is introduced into a hydroforming zone 12. Bydrogen is introduced into zone 12 by way of line 13. Hydro-forming zone 12 is shown diagrammatically and is understood to include all auxiliary equipment, such as catalytic reaction zones, distillation zones, separation zones, solvent extraction zones and the like usually assoalyst employed in the hydroforming zone may be a a platinum-containing catalyst or a molybdenum-containing catalyst or the like although other well-known hydroforming catalysts may be used. Regardless of the type of catalyst employed, there is withdrawn from zone 12 by way of line 14 an aromatic hydrocarbon fraction which may be introduced by way of branch line 15 controlled by valve 16 into a first reaction zone 17 containing a silica-alumina catalyst or may be introduced by line 18 controlled by valve 19 into a second reaction zone 20, also containing a silica-alumina catalyst of the type described. For purposes of illustration, it may be assumed that valve 16 in line 15 is open and the fraction in line 14 is passing thereto and that valve 19 in line 18 is closed for regeneration of the silica-alumina catalyst in reaction zone 20.

The aromatic hydrocarbon fraction having a high acid wash color then passes through bed 21 in reaction zone 17 at the temperature indicated and under the conditions required to maintain a'liquid phase. The product from the reaction zone 17 is withdrawn by line 22 controlled by valve 23 and introduced thereby into a distillation zone 24 which may be a plurality of fractional distillation towers although only one is shown for convenience and simplicity of description. In any event, distillation zone 24 is understood to include all auxiliary equipment usually associated with the modern distillation tower which will include vapor-liquid contacting means, such as bell cap trays and the like, condensing and cooling means, and other necessary equipment connected with a distillation tower, such as known in the oil industry. Distillation zone 24 is provided with a heating means illustrated by a steam coil 25 for adjustment of temperatures and pressures and to allow removal by way of lines 26, 27, and 28 of distillate aromatic solvent fractions as maybe desired, the heavier fractions being discarded from'zone 24 by line 29. These heavy fractions may include polymers, alkymers, and other high boiling materials which may be formed in reaction zone 17 by contact of the feed stock with the bed 21 of silicaalumina catalyst.

It may be assumed that the reaction zone 20 containing a bed 30 of silica-alumina catalyst has shown a loss of activity for treating the fraction in line 14 and the valve 19 is closed to permit regeneration of the silicaalumina catalyst in bed 30 by introduction of a mixture of steam and air through line 31, steam being introduced by opening valve 32 and air being introduced by branch line 333 controlled by valve 34.

After the contaminating bodies have been removed from the bed 3% by burning, with the combustion gases being discarded from zone 20 by line 35 controlled by valve 36, the reaction zone 20 may be placed back on the reaction cycle by opening valve 19, closing valves 36, 32 and 34 and opening valve 37 in line 33 which connects into line 22. V p

The silica-alumina catalyst in bed 21 may be regenerated by closing valve 16 and valve 23 and introducing a mixture of steam and air into reaction zone 17 by way of line 39 through which steam is introduced by opening valve 40 and by opening valve 41 in line 42 to introduce air thereto. The combustion products from zone 17 are removed by line 43 controlled by valve 44.

While an operation has been illustrated wherein aromatic fractions from a hydroforming operation are charged to the process, this is given by way of illustration and not by way of limitation since aromatic, naphthenic, or paraifinic fractions from other operations may be suitably treated in accordance with the present invention. These fractions which contain deleterious bodies usually containing about 4% or less of unsaturated hydrocarbons which may include both the olefins and diolefins, high acid wash color bodies, odor-forming bodies, and other deleterious compounds. The amount of the deleterious bodies may range from about 0.001 to about 4.0 percent by volume of the feed.

In order to illustrate the invention further, a catalyst containing about 88% by weight of silicon oxide and 12% by weight of aluminum oxide and about 0.1% by weight of iron oxide was pilled to form /S-il'lCh diameter pills. The catalyst was heated in a metal reactor to a temperature of 520 F. and a xylene fraction was pumped therethrough in the liquid phase at a pressure of 600 pounds per square inch gauge. The treated Xylene developed considerable color and was distilled to remove the color, polymer and resins. The distilled xylene product after treating 1000 barrels of xylene per ton of catalyst had a 30 Saybolt color and showed an acid wash color of 0 to 1.

Other operations were conducted with. a silica-alumina catalyst pilled to /s inch size. A Xylene fraction was charged to a reaction zone containing the pills at a space velocity of 0.6 v./v./hr., 600 pounds per square inch gauge, and at 525 F. On distilling the product a' 30 Saybolt color product was obtained with low acid wash color. This distilled product had unusual color stability and color did not develop with contact of sulfuric acid over an extended period of time. After extended periods of operation there was no indication of catalyst deterioration.

The aforementioned run was conducted until 3000 barrels of feed stock per barrel of catalyst had been contacted while maintaining a low acid wash color. The temperatures durnig subsequent operations were at 520 F. and pressures of 600 pounds to insure liquid phase operations. The space velocity varied from about 0.6 to about 4.4 v./v./ hr. without any change in acid wash color. After about 3 weeks operation, or afterabout 5000 barrels of feed stock per ton of catalyst is treated, the catalyst loses its ability to remove the color-forming bodies.

To illustrate the desirable operations, the following table shows the effect of treating the xylenes fraction over an extended period of time with the catalyst:

Table I Charge Stock Xylenes l 1 1 1- l- 1'- 1-' 1- 1- 1- 1- 1- 1- 1- 1- 1- 1- 1- 1 1 1 0. 18 O. 11 0. 11 +4 3 3 31. 9 32. 3 32. 1'

It will be seen from the data in the table presented above that over 5000 barrels of feed stock per ton of catalyst contacted the catalyst while maintaining a low acid wash color substantially below 4. This is an unusually desirable result and shows conclusively that the present invention allows long operating times and is commercially feasible. Operations have been continued over a period of 4 months where approximately 2 million barrels of feed stock have been treated with about 100 tons of catalyst with regeneration being carried out in order to maintain high activity after about 2000 barrels of feed stock per ton of catalyst had been contacted. It is not necessary to regenerate the catalyst after only 2000 barrels of feed stock per ton has been contacted but the regeneration periods may be less frequent if so desired. A commercial hexane fraction has been treated for improvement of odor in accordance with the present invention. This fraction was contacted in the liquid phase at a temperature of 430 to 500 F. and at a space velocity of 0.6 v./v./hr. with a bed of 14 to 20 mesh Attapulgus clay. Over a period of 185 hours an equivalent of 1150 barrels of hexane fraction per ton of clay was treated. The product was distilled at a 5 to 1 reflux ratio to remove reaction products. The 2 to 92 percent by volume overhead fraction was found to be of good odor. Inspection of the treated hexane as compared with specification hexane is shown as follows:

Examination of the bottoms fraction disclosed the nature of the reaction occurring on the surface of the catalyst. For example, the 8% high boiling portion showed the presence of alkylated benzene. The undesirable olefins, such as cyclohexene, methylcylopentene and hexene in the hexane fraction, that contributes to undesirable odor in hexane solvents were alkylated with benzene present in the hexane fraction to form hexylbenzene, methyl cyclopentyl benzene and cyclohexyl benzene which were separated from the treated hexane by distillation. Thus suitable aromatic hydrocarbons may be added in a sufficient amount to aliphatic solvents to react with the undesirable olefins to form products which are removable by distillation.

An 87 volume percent cyclohexane fraction was also treated with the Attapulgus clay of the type described before at 500 F. and at 525 pounds per square inch gauge in the liquid phase at a flow rate of 0.4 v./v./hr. The cyclohexane fraction contained about 0.2% by volume of benzene and had a bromine number of 0.6. After 96 hours operation, the total efiiuent shows a bromine number of 0.16 and the benzene content had been reduced to substantially 0. The data show that two olefin molecules were reacting for each molecule of benzene disappearing. Thus, in accordance with the present invention, cyclohexane may be purified to very high purity by removing simultaneously two impurities by reaction with each other.

In the practice of the present invention is is believed that the concentration of unsaturated compounds and polar bodies which tend to form peroxides upon oxidation is substantially reduced. Further it is believed that other contaminating bodies of an unsaturated nature may be removed in accordance with the present invention.

The acid W218i color test referred to herein, namely ASTM test method D-848 47, may be briefly described as a method of testing industrial aromatic hydrocarbons of relatively high purity by agitating three volumes of the aromatic with one volume of concentrated (96:0.5%) sulfuric acid for 20 seconds, permitting the layers to separate, and comparing the color of the acid with a set of standards, which are numbered from 0 (water white) to 14 (the color of half saturated aqueous K CrO The test is an indication of the presence of undesired highly reactive compounds, such as diolefinic materials, which have a tendency to interfere in reactions and processes in which the aromatics may be employed.

The bromine numbers referred to herein were determined by a modified Lewis and Bradstreet method. The numbers are numerically equal to centigrams of bromine consumed per gram of sample.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and to secure by Letters Patent is:

1. A method for producing solvents which comprises contacting a hydrocarbon fraction containing an aromatic hydrocarbon and boiling within the range from about 100 to about 550 F. and also containing unsaturated deleterious bodies in an amount in the range from about 0.001 to about 4.0 percent by volume with a silicaalumina fixed bed of about 7 inch size pills of catalyst at a temperature within the range from about 400 to about 600 F. and at a pressure suificient to maintain a liquid phase, removing the contacted fraction from the catalyst, distilling the contacted fraction to recover a distillate fraction, regenerating the catalyst after about 2,000 barrels of said hydrocarbon fraction per ton of catalyst have been contacted and about 2% by weight of contaminating bodies comprising resins, polymers, polar compounds, peroxides, and the like, have accumulated on the catalyst in a burning operation employing a mixture of air and steam at a temperature of about 800 to about 1000 F. in which a temperature rise of less than 200 F. is obtained to remove said contaminating compounds accumulating thereon during the contacting operation, and then employing said regenerated catalyst to contact additional amounts of said hydrocarbon fraction.

2. A method in accordance with claim 1 in which the hydrocarbon fraction is an aromatic fraction.

3. A method in accordance with claim 1 in which the hydrocarbon fraction is a paraflinic fraction.

4. A method in accordance with claim 1 in which the hydrocarbon fraction is a naphthenic fraction.

5. A method for producing aromatic solvents having a low acid wash color which comprises contacting an aromatic hydrocarbon fraction boiling within the range from about to about 550 F. and also containing unsaturated deleterious bodies in an amount in the range from about 0.001 to about 4.0 percent by volume and having an acid wash color in excess of 4 with a silica-alumina fixed bed of about A inch size pills of catalyst at a temperature within the range from about 400 to about 600 F. and at a pressure in the range from about 400 to about 600 pounds per square inch gauge sufiicient to maintain a liquid phase on said catalyst, said hydrocarbon fraction contacting said catalyst at a l-iquidspace velocity in the range from about 0.25 to about 5 volumes: of hydrocarhon fraction per volume of catalyst per hour, removing the contacted aromatic fraction from the catalyst, distilling the contacted aromatic fraction to recover a distillate fraction having an acid wash color less than 4, regenerating said catalyst after about 2,000 barrels of said aromatic hydrocarbon fraction per ton of catalyst have been contacted and about 2% by weight of contaminating bodies comprising resins, polymers, polar compounds, peroxides, and the like, have accumulated on the catalyst at a temperature in the range from about 800 to about 1000 F. by burning said accumulated contaminating 7 bodies from said catalyst employing a mixture of steam and air in which a temperature rise of less than 200 F. is obtained in said burning operation, and then contacting additional quantitiesyiof said hydrocarbon fraction with the regenerated catalyst. 5 6. A method in accordance with claim 5 in which the aromatic fraction comprises a xylene fraction.

References Cited in the file of this patent UNITED STATES PATENTS Houdry et al Jan. 13, 1936 Hemminger -Q. June 8, 1943 Gutzeit Sept. '4, 1946 Vinyard et a1. Nov. 30,1948 Corson et a1. Mar. 11, 1952 Cornell Dec. 29, 1953 Wankat May 8, 1956 Paull Nov. 6, 1956 

5. A METHOD FOR PRODUCING AROMATIC SOLVENTS HAVING A LOW ACID WASH COLOR WHICH COMPRISES CONTACTING AN AROMATIC HYDROCARBON FRACTION BOILING WITHIN THE RANGE FROM ABOUT 150* TO ABOUT 550*F. AND ALSO CONTAINING UNSATURATED DELETERIOUS BODIES IN AN AMOUNT IN THE RANGE FROM ABOUT 0.001 TO ABOUT 4.0 PERCENT BY VOLUME AND HAVING AN ACID WASH COLOR IN EXCESS OF 4 WITH A SILICA-ALUMINA FIXED BED OF ABOUT 3/16 INCH SIZE PILLS OF CATALYST AT A TEMPERATURE WITHIN THE RANGE FROM ABOUT 400* TO ABOUT 600* F. AND AT A PRESSURE IN THE RANGE FROM ABOUT 400 TO ABOUT 600 POUNDS PER SQUARE INCH GAUGE SUFFICIENT TO MAINTAIN A LIQUID PHASE ON SAID CATALYST, SAID HYDROCARBON FRACTION CONTACTING SAID CATALYST AT A LIQUID SPACE VELOCITY IN THE RANGE FROM ABOUT 0.25 TO ABOUT 5 VOLUMES OF HYDROCARBON FRACTION PER VOLUME OF CATALYST PER HOUR, REMOVING THE CONTACT AROMATIC FRACTION FROM THE CATALYST, DISTILLING THE CONTACTED AROMATIC FRACTION TO RECOVER A DISTILLATE FRACTION HAVING AN ACID WASH COLOR LESS THAN 4, REGENERATING SAID CATALYST AFTER ABOUT 2,000 BARRELS OF SAID AROMATIC HYDROCARBON FRACTION PER TON OF CATALYST HAVE BEEN CONTACTED AND ABOUT 2% BY WEIGHT OF CONTAMINATING BODIES COMPRISING RESINS, POLYMERS, POLAR COMPOUNDS, PEROXIDES, AND THE LIKE, HAVE ACCUMULATED ON THE CATALYST AT A TEMPERATURE IN THE RANGE FROM ABOUT 800* TO ABOUT 1000*F. BY BURNING SAID ACCUMULATED CONTAMINATING 